The potential of selected proteins of human cytomegalovirus (HCMV) to induce a helper T (Th) cell immune response was investigated in healthy HCMV-seropositive donors. Recombinant derived glycoproteins B (gpUL55), H (gpUL75), integral membrane protein (pUL100), the US6-US11 glycoprotein family (pUS6-US11), the matrix proteins pp65 (ppUL83), pp28 (ppUL99) and the immediate early proteins IE1 (pUL123), IE2 (pUL122) and UL69 (pUL69) were used as stimulating antigens in a lymphocyte proliferation assay. The antigen-specific proliferative response was measured in HCMV-specific T cell lines (phenotype CD4+ CD8-) generated from five donors by stimulation of peripheral blood mononuclear cells with purified HCMV or HCMV-infected fibroblasts. A proliferative T cell response was induced by pp65, gB, gH, IE1, IE2 and UL69, with a dominant response to pp65 in all donors. Three T cell lines responded to gB and gH, respectively. For IE1, IE2 and UL69 a T cell stimulation could be demonstrated in single cell lines generated with lysate of HCMV-infected fibroblasts.